Method and apparatus for power amplification



March 29, 1932. M. E. THOMPSON 9 METHOD AND APPARATUS 'FOR POWER AMILIFICATION Filed June 4, 1927 E L M Patented Mar. 29, 1932 PATENTOF-RICE" mom a. rnourson, or runaway, msnvam mmion AND nrmarus nonrowan. mmicarroir Application m a June 4,1927. Serial I'm 198,4 9.

My invention is concerned with a new method of using thermionic currentsin pow- Y en amplification and with novel apparatus adapted for use inpracticing the method.

6' When a magnetic field is impressed at" right angles to th path of anelectron stream,

the electrons ar deflected in a direction perpendicular both to thedirection of the m%:

net field and to the electric field causing .t e

electron flow, the ma itudeand direction of the deflection depen ingupon the strength and relative direction respectively of the two fields.

- My invention comprises a method for utilizing, and apparatus forapplyin ,thls

phenomenon in power amplification o a1ternating or otherwise var ingcurrents. I

cause thecurrent that is to team lified to create an electromagneticfield at right angles to 2 the flow of electrons from a heated cathode oa plurality ofpositively charged anodes. I

place a shield or shields between the electrodes in such a way as tointercept a part of the electron flow to the various anodes andpreferabl insuch a way as to insure that each ano e receivessubstantially equal current from the heated cathode when the magneticfield strength is zero. The deflection of the electroniccurrentoccurring when the 80 magnetic field is not zero is made to causea change in the distribution of the electronic current to the variousanodes without changing substantially the total current received b allof the anodes. In this manner an clianges in the direction of strengthofthe controlling current, that is in the current which creates themagnetic field and therefore determines its strength and direction,

are reflected in changes in the currents in the various anode circuits.a

a The modern practice as exemplified in the use of the well-knownthree-electrode vacuum tube varies the strength of the current tothe-anode in response to changes in an electrostatic field applied tothe grid. As outlined above my ethod comprises the maintenance ofa subsantiallyconstant current with its distribution varied in response.

to changes inlan electromagnetic field. This "radical departure from themodern practice results in the elimination of some of the in-,herent-disadvantages of the three-electrode tube and also results in'certain economies in operation all of which will become apparent fromthe following description of the appal5 ratus and its operation.

For a better understandin of my invention reference should be ha to theaccompanying drawings of which Figs 1a, 1b. and

1c illustrate diagrammatically the fundamental principles of myinvention. Fig. 2

is a cross-sectional view of the preferred form of a vacuum tubeconstructed to operate according to my invention, and- Fig. 3illustrates diagrammatically one application,

of my amplifying device.-

In Eigs. 1a, 1b and 1c, 1 is a coil adapted to carr alternating current;2 is a filament heated y a battery 3 to which it is connected b leads 4;5 and 6 are shields of any" suita le"mate rial and 7 and 8 are metalinclosed within an evacuated chamber. It is immaterial whether or notthe coil 1 is within this chamber. If no current is'flowing in so coil 1then the distribution of the electrons from the filament to the platesand shields will be as shown by the broken lines 28 in Fig. 1a.- Therewill of course be electrons emitted radially in 'all directions from thefilament but only that part of the stream indicated is material to thisdescri tion. The plates, being symmetrically locate with respect to theshields and ament and being at equal otentials with res ect to thefilament WiIi each receive equa electronic current. If new a current issent through the coil 1 in an anti-clockwise direction, a magnetic fieldat right angles to the paper and with its positive direction upward fromthe Eaper will be impressed within the coil. eld will deflect theelectronic current to the left so that the plate 8 will receive currentover a larger area, and the plate 7 over a smaller area, than when nocurrent is flowlng in the coil 15 thetotal current to both of the platesbeing substantially the same in either case. With increasinganti-clockwise current in the coil 1, the current to plate v7 5 andthrough impedance 9' decreases and the current to plate 8 and throughimpedance 1O correspondingly increases. A ma et1c field strengthsufiicient to deflect all the avallable electronic current to plate 8 isshown in 10 in icated by 29. Fig. 1a illustrates similarly the extremecase when all of the available electronic current is received by plate 7under a field impressed by current flowing in a clockwise direction incoil 1. With a ternatin or pulsating current through coil 1 the eectronic current will therefore be deflected synchronously with thecurrent in the coil first to one late and then to the other; the currentto p ate 7 decreasing while that to plate 8 is increasing and viceversa.

To utilize the general principles illustrated in Figs. 1a, 1b and 10 anarran ement such as shown in Fig. 2 is preferre An evacuated glass tubeor bulb, shown in crosssection at 12 is surrounded by the coil 1. Thefilament 2, within the tube and along the axis of the coil, is heated bycurrent led to the filament b wires 4 from the battery 3. The lead wiresrom'the battery to the filament would be in practice of courseintroduced into the tube at one end in the usual manner.

The filam'erit 3 is surrounded by a cylindrical shield within the tubeand having a comparatively small diameter. The shield is provided withlongitudinal slots 13 of uniform width which, in the embodimentillus-.trated, arefour' in number and of approxi- 9 mately equalcircumferential width with the section of the shield between the slots.The

anodes are'formed of separated segments 7 and 8 of a second cylindercoaxial with the shield and of a substantially greater diam- 45 eter;the number of segments being twice that of the slots 13. The spacing ofthe segments issuch that the arc subtendedv by any slot 13 or section ofthe shield 5' subtends approximately one-half of each of two neigh- 50borin anodes 7 and 8. The'anodes 7 are in electrical contact throughwires 14 and the anodes 8 are in electrical contact through wire 15. Theanodes 7 and 8 are connected through equal impedances 9 and 10 res c- 55tively with the positive terminal of the attery 11 which in turn isconnected at its negative terminal with the battery 3. The particularmethod of supporting the anodes,

shield andfilament within the tube, or in 60 making the electricalconnections is immaterial to my invention and may be done in anywell-knownmanner. -The axial length of the anodes and shield arepreferably equal to or greater than that of the filament and 05substantially less than thatof the coil 1.

Fi 1b; the deflected electron stream being eanne The operhtion of theapparatus of Fig. 2 is similar in all respect wit that already describedin connection with Fi s. 1a, 1b and 10 the only difference being t atthe cylindrical arrangement permits a reater pro- 7 portion of theelectrons given oi? by the filament to contribute to the total current.The distribution of this electronic current when no current is flowingin the coil 1 is shown by the broken lines 28 radiatin from thefilament; the curved lines 29 in icating the path of the electrons whendeflected entirely to plates 8 by a clockwise current in coil 1 ofmaximum strength for the design of the particular tube. For simplicitythat art of the stream of electrons intercepted y the shield. 5 is notillustrated. I

In the. operation of such a tube as that illustrated in Fig. 2 it ishighly desirable that the filament temperature be, maintained low enoughto insure that the lowest potential applied to the plates will besufiicient to draw to the plates all of the electron current passingthrough the slots 13. If the filament temperature is thus restrictedsubstantially constant total plate current is obtained and variations inthe current in coil 1 are proportionately reflected in variations in thecurrents through impedances 9 and 10. In practice, the impedances 9 and10 will form the primary of a transformer, the secondary being soconnected that decreasing current in impedance 9 will affect thesecondary voltage in the same direction as increasing current inimpedance 10.

The use of a lower filament temperature than that usually employed inthe three-electrode tubes results in a substantial increase in the lifeof the tube and in additional economy in the size of the battery 3, thatis in the so-called A battery necessary to supply the filament current.iDue'to the fact that a tube operated according to my invention passes aconstant plate current, the internal resistance of the tube is constantand the errors due .to changing tube resistance usually occurring in themodern tubes are eliminated. Furthermore, the internal capacity eflectswhich now comprise perhaps the most serious drawback of the threeelectrode tubes are eliminated by a tube such as that in Fig. 2 as inoperation the capacity between the two sets of plates and the otherelements of the tube will always balance each other due to the fact thatthe potentials at the two sets of plates rise and fall oppositely. Theshields 5 may be grounded or given a slight positive-0r negativepotential as desired and as is found preferable for the particular tubeand for the particular use to which the tube is put.

In Fig. 3 I have shown diagrammatically two amplifying stages of a radiocircuit employing a tube such as that of Fig. 2. For convenience thetube is shown symbolically u cuit controls the filament temperatures.

' terminal of the B assume ary of transformer18 due to the receptionfilament 2 and a coil 1. The shield is notillustrated and the variouselements are now shown in their relative positions. The A battery, 3,supplies current in parallel to the filaments 2. As in the otherfigures, the plates 7 and 8 are connected through impedances 9 and 10respectively to the positive battery 11, the negative terminal of whichis connected to the positive terminal of the A battery. An adjustableresistance 16 in the A battery antenna 17 or other receiver ofelectromag-' netic waves, is connected through the primary winding ofatransformer 18 to a ground 19 as in the usual receiving circuit. Thesecofflialctromagnetic waves by the antenna.

"illustrated the preferred form of apparatus ondary winding of thetransformer 18 is connected through a variable condenser 20 andinductance 21 with the terminals of the coil 1 of the first tube. Theinductance 21 is shown as a separate element. It may. of course, ifdesired form part of the coil 1. The impedances Qand 10 of the platecircuits of the tube form the primary windings of a transformer 22 thesecondary windings 23 and 24 of which are connected with the coil 1' ofthe second tube through the usual capacity and inductance elements; thewinding 23 being coupled with the impedance 9 and the winding 24 beingcoupled with the impedance 10. Similarly the impedances 9 and 10'associated with the plates 7 and 8' of the second tube are coupled withsecondary windings 23 and'24' of a transformer 22'.

i The filament circuit is grounded through a connection 25 with thelower end of the antenna circuit and the secondary circuits of thetransformers are likewise grounded through connections 26 leading to thewire 25. In each of the connections 26 is a resistance 27.

In operation of the circuit of Fig. 3 electromagnetic waves received bythe antenna 17 induce alternating voltage in thesecondary winding of thetransformer 18, causing alternating current to flow through the coil 1andresulting in an alternating magnetic field within the first tube. 1The alternating field causes variations in the currents throughimpedances 9 and 10 in opposite directions as heretofore explained. Thecoupling of the transformer 22 is such that currents varying oppositelyin coils 9 and 10 induce voltages in coils 23 and 24 in the samedirection. The

current in coil 1 caused by the voltages in-,

riations in voltage occurring in the secondembodying the principle of mynew method of using thermionic currents in power amplification. I havealso shown one application of such apparatus. My invention is notlimited, however, to any particular application nor to the particulardesign of tube illusave now described my invention and trated. I believe.I am the first to control the distribution of an electronic current byvariations in a magnetic fieldin amplifyin devices and as such amentitled to a broa interpretation of my claims. The term al ternatingcurrent as employed in my claims is intended to include'broadly anyvarying current as distinguished from constant direct current and is notintended to' limit my device to the amplification of sinusoidalcurrents.

I claim:

1. The method of amplifying alternating currents which consists increating a radial electron flow from a heated cathode to a plurality ofanodes equidistant therefrom and positively charged with respect theretoand in controlling the dlStIlbHtIOIl of said flowv to the anodesresponsive to changes in a magnetic field created by the current to'beam: plified, while maintaining substantially constant the totalelectronic current received by all of said anodes.

2. In combination with a vacuum tube having a heated cathode and apluralityof positively charged anodes, a cylindrical coll adapted tocarry alternating current, and surrounding said cathode and anodes andso located with respect thereto as to impress a magnetic fieldat-right'angles to said elec- 1y with respect thereto to receive theelec-' tronic current therefrom, means within said 1 tube forintercepting a part of said electronic current, means for creatinganalternating magnetic field at right angles to the electronic currentandvarying with the current to be amplified. v x I 4. The combinationcomprising a vacuum tube having a heated cathode for the emission' of anelectron flow and a plurality of anodes radially disposed with respectto said cathode for the reception of a constant frac-' tion of saidelectron flow, a source of electrical energy for charging said anodespositively with respect to said cathode, connections between said anodesand said source each rovided with equal impedances, and a cylin ricalcoil adapted to carry. alternating current to be am lified and solocated as I to impress a mafgnetic field at right angles to saielectron ow.

5. An alternating current amplifying device comprising in combination anevacuated vessel, a filament within said vessel adapted to-be heated toemit an electronic current, a cylindrical shield within said vessel andsurrounding said filament, said shield being provided with axial slotsof equal width, a plurality of separated electrically conducting anodesforming a longitudinally interrupted cylindrical surface about saidshield and coaxial therewith, said anodes being of approximately equalarea and of twice the number of the slots in said shield, electricalconnections between alternate anodes, 6 means external to said vesseland connecting through the walls of said vessel with two electricallyseparated anodes for charging said anodes ositively with respect to saidfilament, and a cylindrical'coil coaxial with said filament adapted tocarry the current to be amplified whereby a magnetic field varying withsaid current may be impressed upon the electronic current to deflectsaid electronic current and thus to vary the distribution of saidelectronic current to said anodes responsively with changes in thecurrent to be amplified.

6. Apparatus as in claim 5 wherein equal impedances forming the primaryof a transa former coil are rovided in the connecting lines between saidexternal means and said electrically separated anodes.

7. Apparatus as in claim 5 wherein the anodes are so located withrespect to the shield 4 that radii from the filament to the s acesbetween neighboring anodes bifurcate 0th the axial slots of the shieldand the sections of the shield between the slots.

In testimony whereof, I have signed my name to this specification. v

MILTON E. THOMSON.

